Staphylococcus aureus produces a number of enterotoxins (SEs) which are the causative agents of staphylococcal food poisoning. The genes for SEs are located on plasmids, phages and other potentially movable genetic elements such as pathogenicity islands, further increasing their possible spread to other organisms in the environment. Staphylococcal enterotoxin B (SEB) is an NIAID Category B Priority agent and is generally produced at much higher levels than other SEs by toxigenic S. aureus strains. Furthermore, the levels of SEB produced by different S. aureus strains are highly variable. Recent studies suggest that SEB may regulate the synthesis of other extracellular proteins including virulence factors, thereby affecting staphylococcal virulence. The goal of this Exploratory/Developmental proposal is to study the gene expression and proteomic profiles of various SEB-producing S. aureus strains and to further test the hypothesis that expression of SEB by S. aureus strains may affect the production of intracellular and extracellular proteins, including other toxins and virulence factors. This will be accomplished by a comparative genomic analysis of different SEB-producing strains utilizing S. aureus microarrays provided to us by NIAID through TIGR/PFGRC. We will also study the cellular gene expression profiles in these strains using microarrays. The effect of SEB on global gene expression in isogenic S. aureus strains will also be studied utilizing the microarray technology. We will also study the proteomes of SEB-producing S. aureus strains as well as pairs of isogenic SEB-positive/SEB-negative strains by two-dimensional Difference Gel Electrophoresis using fluorescence dyes. Differences in the protein content and levels of particular proteins in these strains will be identified by mass spectrometry. Successful completion of these studies will provide a solid basis for future analysis of the molecular mechanisms involved in the regulation of SEB production, and its effect on staphylococcal gene expression and pathogenesis.